At 03:01 PM 3/12/2004 -0500, you wrote:
>-List,
>Anyone here ever measure very low temperatures (-100=BAC) by measuring=20
>Vforward for a given Iforward?
>There are several high dollar diodes out there (GaAlAs, GaAs, and Si) that=
=20
>are extremely well characterized and thus good for the task, but I'm=20
>trying to stay on the cheap here.
>
>Does anyone have any data about Vforward vs Temp for a common (i.e. cheap)=
=20
>Si diode at very low temperatures?
>
>I've been googling for a day and a half now on this project with limited=20
>success.
>Thanks in advance.
>Robert Mash
>740.592.2655

You can use an ordinary Si diode, and dV/dT is pretty constant with constant
current, provide you stay above about 100K in temperature (a bit lower
than that, IIRC).

If you have a library at hand, check out:

Review of Scientific Instruments Vol 65(10) pp. 3289-3290. October 1994

I prefer to use thermocouples when possible. They are relatively cheap,=
 rugged
and no harder (to be fair, no *easier* also) to use at -150'C than at=
 +200'C.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the=
 reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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